Vehicle brakes require periodic adjustment as the lining wears, and a number of automatic adjusters have been designed wherein the brake operating structure automatically compensates for such wear. Some adjusters operate when the vehicle is braked while in reverse, and in heavy duty vehicles, such as trucks and semi trailers, the brake slack adjusters are often incorporated into actuating members interposed between a brake rod and the brake operating shaft. The invention is particularly directed to brake slack adjusters of the type used with heavy duty vehicles, and constitutes an improvement over the brake slack adjuster disclosed in the assignee's U.S. Pat. No. 3,921,765.
Heavy duty automatic brake slack adjusters are known to utilize unidirectionally driven worms for rotating a worm gear, which, through appropriate mechanism, incrementally adjusts that portion of the brake actuator directly connected to the brake operating shaft. The worm drive unit may be connected to the vehicle brake actuating rod in such a manner that a motion is supplied to the actuator mechanism each time the brakes are actuated, but due to lost motion apparatus adjustment of the slack take-up occurs only when sufficient brake wear has occurred to permit sufficient movement of the adjusting apparatus. Typical brake slack adjusters of the aforementioned type are shown in U.S. Pat. Nos. Re. 26,965; 3,261,433 and 3,428,154.
In the assignee's U.S. Pat. No. 3,921,765 an automatic brake slack adjuster is disclosed of the aforementioned type, and the invention improves upon such apparatus by simplifying the structure, providing improved unidirectional drive and holding characteristics, simplifying the manual preadjustment procedure, and minimizing the necessity for special hardware directly associated with the brake actuating rod and yoke connected to the brake adjuster.
It is an object of the invention to provide an automatic vehicle brake slack adjuster of relatively simplified construction capable of automatically adjusting vehicle brakes in accordance with brake wear.
A further object of the invention is to provide an adjuster for vehicle brakes which may be readily operated and preadjusted without requiring special skill, and wherein an extended operating life is achievable due to "lifetime" lubrication sealing.
Another object of the invention is to provide an automatic brake slack adjuster employing a universal bracket with its operating linkage which eliminates the necessity for special hardware or modification of the vehicle brake operating rod or fittings.
In the practice of the invention the adjuster includes a body interposed between the vehicle brake operating rod and the brake operating shaft. The adjuster incorporates a worm drive unit connected to the brake rod by a bracket at a location spaced from the primary pivotal connection between the adjuster and brake rod whereby movement of a linkage occurs during each braking cycle. The worm drive incorporates unidirectional clutch means rotating a second worm drive unit through a displaceable worm gear which, when disengaged from its associated worm, permits preadjustment or major adjustment, by means of a conventional socket wrench connection. The placing of a socket wrench upon the second worm shaft automatically disengages a worm gear from the worm of the first drive unit, and removal of the wrench socket automatically permits worm and worm gear reengagement.
The linkage associated with the first worm drive unit utilizes a bracket pivotally connected to the primary adjuster-brake rod pivot pin, and this bracket includes a pivot spaced from the primary pivot pin opening and a slot for receiving the brake rod. Thus, the slot assures proper orientation of the bracket to the brake rod, and motion is transmitted to the adjuster linkage during each braking cycle without modification to the brake rod, brake rod yoke, or other standard vehicle components.